1. Field of the Invention
The present invention relates generally to the field of information storage devices, and more particularly to head gimbal assemblies used in information storage devices.
2. Background of the Art
Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read are referred to as “read heads” herein, regardless of other devices and functions the read head may also perform (e.g. writing, micro-actuation, flying height control, touch down detection, lapping control, etc).
In a modern magnetic hard disk drive device, each read head is a sub-component of a head gimbal assembly (HGA). The read head typically includes a slider and a read/write transducer. The read/write transducer typically comprises a magneto-resistive read element (e.g. so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element) and an inductive write structure comprising a flat coil deposited by photolithography and a yoke structure having pole tips that face a disk media. The typical read/write element requires four electrical connection terminals (i.e. so called “bond pads”) on the read head. These four do not including any additional bond pads that may be required for the manufacture and/or testing of the read head, such as bond pads for an electrical lapping guide (ELG) on the read head to control lapping of the pole tips during manufacture.
The HGA typically also includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the bond pads of the read head. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flex cable. The plurality of HGAs is attached to various arms of the actuator, and each of the laminated flexures of the HGAs has a flexure tail that is electrically connected to the HSA's flex cable. Modern laminated flexures typically include electrically conductive copper traces that are isolated from a stainless steel support layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flex cable on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along the actuator arm and ultimately attaches to the flex cable adjacent the actuator body. That is, the flexure includes electrically conductive traces that extend from adjacent the head and terminate at electrical connection points at the flexure tail. At the other end, the electrically conductive traces are electrically connected to a plurality of electrically conductive bonding pads on the head.
The industry trend towards increasing areal data density has necessitated, for certain disk drive products, that additional features be added to the read head. Each such additional feature requires electrical connection to additional bonding pads per read head. For example, a microactuator for fine tracking control may be added to the read head to increase servo bandwidth and thereby facilitate an increase in the data track density of the disk drive (typically measured in tracks per inch). A heater for flying height actuation may also be added to the read head to allow the separation between the read head and the disk media to be greater when not reading or writing (and thereby improving tribological performance of the read head), while causing thermal expansion that temporarily brings the read/write transducer closer to the disk media while reading and writing (and thereby obtain acceptable signal amplitude). Also, a touch-down sensor may be added to sense when the read head contacts the disk surface during operation.
However, in most applications, the head cannot be made larger to accommodate the additional bonding pads associated with such improvements. On the contrary, as a general trend, heads have become smaller for various important reasons (e.g. cost, dynamic response to mechanical shock, etc), and such trend is unlikely to reverse. Although some number of additional bonding pads might be accommodated by making the bonding pads smaller, the size of bonding pads in contemporary read/write heads has already been reduced to the point where electrical interconnect during manufacture has become challenging and difficult. Accordingly, there is a need in the art for HGA designs that can facilitate the practical electrical connection of conductive traces of the flexure to more bonding pads on the head.